#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
int g_val = 100;
int main()
{
    pid_t id = fork();
    if(id == 0)
    {
        int cnt = 5;
        while(1)
        {
            printf("I am child, pid: %d, ppid: %d, g_val: %d, &g_val: %p\n", getpid(), getppid(), g_val, &g_val);
            sleep(1);
            if(cnt)
            {
                cnt--;
            }
            else
            {
                g_val = 200;
                printf("子进程change g_val: 100 -> 200\n");
                cnt--;
            }
        }
    }
    else 
    {
        while(1)
        {
            printf("I am parent, pid: %d, ppid: %d, g_val: %d, &g_val: %p\n", getpid(), getppid(), g_val, &g_val);
            sleep(1);
        }
    }
    return 0;
}

